[Numpy-discussion] mean of two or more arrays while ignoring a specific value
David Warde-Farley
dwf@cs.toronto....
Tue Jul 14 14:59:01 CDT 2009
On 14-Jul-09, at 3:33 PM, Greg Fiske wrote:
> Dear list,
>
>
>
> I'm learning to work with numpy arrays. Can somebody explain how to
> get the
> average of two separate arrays while ignoring a user defined value
> in one
> array?
>
>
>
> For example:
>
>>>> a = numpy.array([1,5,4,99])
>
>>>> b = numpy.array([3,7,2,8])
>
>
>
> Ignoring the value 99, the result should be an array like c=
> ([2,6,3,8])
The simplest way I can think of doing it:
In [60]: c = concatenate((a[newaxis,:], b[newaxis,:]),axis=0)
In [61]: c = where(c == 99, nan, float64(c))
In [62]: nansum(c,axis=0) / (~isnan(c)).sum(axis=0)
Out[62]: array([ 2., 6., 3., 8.])
The last line could be replaced with scipy.stats.nanmean(c, axis=0) if
you have scipy installed.
David
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